Picture of small river
Latest Outlook
Summary map for May 2023 Hydrological Outlook

May 2023 Hydrological Outlook

Period: From May 2023      Issued on 10.05.2023 using data to the end of April 2023

The outlook for the May-July as a whole is for river flows and groundwater levels to be normal to above normal across the majority of the UK. For May, normal to below normal flows are likely in northern Scotland. River flows and groundwater levels in southern England are likely to be above normal for May.


Rainfall for April was below average in north-western parts of the UK and Wales and above average in south-eastern England and northern Ireland. More than 170 percent of average rainfall fell over Kent, whilst the majority of Scotland saw less than 90 percent of average.

The forecast (issued by the Met Office on 1.5.2023) shows an increase in the likelihood of wet conditions (1.5 times the normal chance) for the May, June, July period compared to normal, with a decreased likelihood (0.5 times the normal chance) that May-June will be drier than normal.

River flows:

River flows in April broadly followed the precipitation pattern. Below normal and notably low flows were recorded in northern Scotland. Normal flows were seen across the majority of southern Scotland and northern England. Above normal, notably high and exceptionally high flows were recorded across southern England and Wales, with record breaking high flows seen on the Medway and Ouse.

The forecast for May is for this pattern to continue, with normal to below normal flows expected in northern Scotland, and above normal flows being likely in southern England. For the rest of the UK normal to above normal flows are expected over the next three months.


Groundwater levels in April were generally normal to above normal, with some below normal levels recorded in eastern Scotland and at Dalton Holme on the Humber Estuary. Levels in central southern England were notably to exceptionally high in several boreholes in the chalk and Jurassic limestone aquifers.

The forecast for May, and the May-June-July period is for normal to above normal levels to persist across the majority of boreholes, with a few localised exceptions where levels could drop to slightly below normal.